The present invention relates to an auxiliary drive of an internal combustion engine for an air compressor. The compressor has a piston that is guided in a cylinder and that is driven via a connecting rod by a crankshaft. The crankshaft is connected to a drive gear wheel, which is driven by the drive shaft of the internal combustion engine by means of gear wheels. The air compressor drive gear wheel meshes with a gear wheel on the camshaft.
The gear wheel drive of piston compressors, which are used, among other things, for providing compressed air for commercial vehicles that have air brakes, has a series of advantages. The most important advantage, when compared with the earlier frequently used V-belt drives, is that gear wheel drives are completely maintenance-free. This advantage gains in importance due to the fact that a steering hydraulic pump is often driven by the air compressor crankshaft; this further increases the requirement for maximum possible operating reliability of the air compressor drive, which is optimally possible only by using gear wheels.
The piston compressor type of construction has proven to be very expedient for use in the case of brake air compressors. However, the disadvantage of using a gear wheel drive is that the compressed air that remains in the cylinder clearance of the air compressor once the top dead center has been reached expands, as a result of which the tangential force that drives the air compressor suddenly becomes negative and the air compressor releases torque. This leads to a sudden flank change in the tooth mesh accompanied by an unpleasant banging noise.
It is not always possible to reduce this noise to an acceptable level, particularly in the case of lightweight drives as are used in modern high output engines, even when the rotating flank clearance between the air compressor gear wheel and the driving camshaft gear wheel is manufactured or adjusted to low values. The reason for this lies in the fact that the drive torque of the camshaft also varies greatly, particularly in the case of engines having a small number of cylinders, and may even have negative components. If there is an overlapping of the negative torque of the air compressor in the phase of reexpansion with small or even negative torque of the camshaft, then in addition to the air compressor gear wheel there is also a reverse acceleration of the camshaft gear wheel, which is transmitted as a jolt to the rest of the gear drive.
It is not possible to consider removing this disadvantage by means of a large increase in the rotating masses of the air compressor and the camshaft gear wheel for reasons of low costs, limited structural space, and low weight. The increase in the moment of inertia would have to be considerable and therefore expensive heavy, and space-consuming, since the disturbing noises occur particularly during idling. However, due to the low idling speed, the kinetic energy of the rotating masses is low in this operating condition.
It is therefore an object of the present invention to form the drive in such a way that with a low moment of inertia, small dimensions, and a light construction of the rotating masses of the air compressor and of the driving camshaft gear wheel, the reverse acceleration of the camshaft gear wheel is prevented and the knocking pulse and noise in the mesh of the camshaft gear wheel is minimized.